DPSIR - Building Ecosystem Models of Everything, Including the Kitchen Sink

Ecosystem based management represents a new stage in the development of ecosystem models. H.T. Odum’s ecosystem model of Silver Springs is the acorn from which mighty oaks have grown. Odum created this, the first ecosystem model, in the 1950s as a tool to synthesize information from disparate types of data and to illustrate the underlying processes at work in ecosystems. Later, beginning in the 1980s, ecosystem models found wide application in risk analyses related to the implementation of the Clean Water Act. Today, ecosystem models provide the comprehensive framework that managers use to assess environmental problems, often spanning large regions, and to evaluate proposed solutions.

With maturity and widespread application, changes in ecosystem models have followed an arc of increasing scope and complexity. As the acorn is to the oak, Odum’s Silver Springs model is tiny in scale and shares only the most rudimentary elements in common with today's model. Ecosystem based management defines an ecosystem as “a geographically specified system of organisms (including humans), the environment, and the processes that control its dynamics.” Where Odum’s model described the Silver Springs ecosystem simply, in terms of material and energy budgets, today ecosystem models must describe everything in a region - including people - and their kitchen sinks.

The DPSIR framework represents the latest form taken in the continuing growth and development of ecosystem models. DPSIR stands for Driver-Pressure-State-Impact-Response.

Drivers are factors that result in pressures that in turn cause changes in the system.

Pressures include factors such as coastal pollution, habitat loss and degradation, and fishing effort that can be mapped to specific drivers.

State variables are indicators of the condition of the ecosystem (including physical, chemical, and biotic factors).

Impacts comprise measures of the effect of change in these state variables such as loss of biodiversity, declines in productivity and yield, etc.

Responses are the actions (regulatory and otherwise) that are taken in response to predicted impacts.

Recently, Atkins et al. (2011) argue that the needs of ecosystem based management can be met by incorporating the concept of ecosystem services into ecosystem models constructed around the DPSIR framework. The approach described by Atkins et al. brings people more fully into the picture by addressing management responses directly and by using ecosystem services to evaluate impacts. DPSIR has been applied broadly in environmental assessments of terrestrial and aquatic ecosystems, especially in Europe. But, the jury is still out on the question of whether ecosystem models built around the DPSIR framework are yet sturdy enough to support regional management of coastal ecosystems.